DC to DC converters are frequently employed to convert relatively low voltage DC sources into high voltage DC sources. The high voltage DC source is then suitable for application to a DC load, such as electrodes of an electron tube or other electrical device.
FIG. 3 is a circuit diagram of a typical DC to DC converter. The DC to DC converter 100 includes a first DC input 110 connected to a first DC power supply (not shown), a second DC input 120 connected to a second DC power supply (not shown), a transformer 130, a first switch transistor 140, a second switch transistor 150, a pulse generator 160, and a pulse width modulation (PWM) circuit 170. The transformer 130 includes a primary winding 131, a sub-primary winding 132, and a secondary winding 133. The PWM circuit 170 includes an output 171 configured to provide a square pulse. The pulse generator 160 includes an input 161 and two outputs 162, 163. The first and second switch transistors 140, 150 are N-channel metal-oxide-semiconductor field-effect transistors (N-MOSFETs).
The first switch transistor 140 includes a source electrode “S”, a drain electrode “D”, and a-gate electrode “G”. The source electrode “S” is connected to ground via a resistor 141. The drain electrode “D” is connected to the first DC input 110 via the primary winding 131 of the transformer 130. The gate electrode “G” is connected to the output 162 of the pulse generator 160.
The second switch transistor 150 includes a source electrode “S”, a drain electrode “D”, and a gate electrode “G”. The source electrode “S” is connected to ground. The drain electrode “D” is connected to ground via the sub-primary winding 132 of the transformer 130 and a capacitor 151 in series. The gate electrode “G” is connected to the output 163 of the pulse generator 160.
The input 161 of the pulse generator 160 is connected to the output 171 of the PWM circuit 170 for receiving the square pulse. The pulse generator 160 generates two pulse driving signals with opposite phases according to the received square pulse, and provides the two pulse driving signals through the two outputs 162, 163 respectively.
The second DC input 120 provides operation voltages respectively to the pulse generator 160 and the PWM circuit 170.
When the pulse driving signal at the output 162 of the pulse generator 160 is a high level voltage and the pulse driving signal at the output 163 of the pulse generator 160 is a low level voltage, the first switch transistor 140 is turned on and the second switch transistor 150 is turned off. Thus a first current path is formed sequentially through the first DC input 110, the primary winding 131 of the transformer 130, the first switch transistor 140, and the resistor 141. A first current is formed when the first DC power supply provided to the first DC input 110 is connected to ground via the first current path. The first current flowing through the first current path linearly increases until the electromagnetic induction generated in the primary winding 131 reaches a predetermined maximum threshold.
When the pulse driving signal at the output 162 of the pulse generator 160 is a low level voltage and the pulse driving signal at the output 163 of the pulse generator 160 is a high level voltage, the first switch transistor 140 is turned off and the second switch transistor 150 is turned on. Thus a second current path is formed sequentially through the capacitor 151, the sub-primary winding 132 of the transformer 130, and the second switch transistor 150. Thus energy stored in the primary winding 131 of the transformer 130 transfers to the sub-primary winding 132 and discharges to ground through the second current path. Therefore a second current is formed and flows through the sub-primary winding 132 when the energy is discharged.
When current flows through the primary winding 131 or the sub-primary winding 132, electromagnetic induction at the secondary winding 133 generates an alternating current (AC) voltage between two outputs 3, 8 of the secondary winding 133. Then the AC voltage is rectified, and transformed to a DC voltage. The DC voltage is then used for driving a load circuit (not shown).
In general, the pulse generator 160 is an expensive component. Thus the cost of the DC to DC converter 100 is correspondingly high.
It is desired to provide a new DC to DC converter which can overcome the above-described deficiencies.